Most inkjet printers dispense colorants or inks that are comprised of a dye and/or a pigment that is either dissolved or suspended in a volatile solvent. When the print head of the printer deposits the colorants on a recording media such as paper or film, the solvents in the colorants quickly evaporate, leaving the dyes and/or pigments behind on the recording media.
During the manufacturing process printheads for inkjet printers must be tested. Accordingly, it is customary to provide an inkjet printhead with a dye and/or pigment based colorant that will be dispensed from the printhead as a test to ensure that the printhead functions properly. It may also be necessary to include a colorant with a printhead so that a printer in which the printhead is installed may be tested.
However, where colorants are allowed to remain in a printhead for extended periods of time, it is often the case that the volatile solvents that make up the colorants will at least partially evaporate, leaving within the nozzles of the print head a residue of particles or a precipitate. FIGS. 1a-1c illustrate how the evaporation of a volatile solvent from the colorant can result in the malfunction of the printhead.
FIG. 1a is a schematic view of a typical nozzle 12 in an inkjet printhead 10. As will be readily understood by those skilled in the art, a printhead 10 typically includes multiple nozzles 12, each of which is connected to a reservoir (not shown) by a conduit 14. Generally, a single conduit 14 will supply colorant 13 to multiple nozzles 12. In a thermal inkjet printhead, a small resistor 16 will be provided adjacent to the opening of the nozzle 12. The resistor 16 ejects colorant 13 from the nozzle 12 by rapidly raising the temperature of the colorant 13 so as to cause the solvent thereof to boil. The rapid expansion of the boiling solvent ejects a droplet (not shown) of colorant 13 from the opening of the nozzle 12 in a known manner. Other types of inkjet printheads may utilize a piezoelectric element in lieu of the resistor 16.
The printhead 10 illustrated in FIG. 1a represents a printhead that has been newly filled with the colorant 13. FIG. 1b, represents a printhead 10 that has been stored for a period of time. Over time the solvents present in the colorant 13 begin to evaporate as represented by arrows 18. The evaporation of the solvents from the colorant 13 concentrates the pigments and/or dyes present in the colorant 13. As more time passes, the pigments and/or dyes begin to form a solid accretion 2. As can be seen in FIG. 1c, the accretion 2 has grown to the point where it blocks the nozzle 12, thereby preventing its proper functioning.
In order to retard the evaporation of the solvents from a colorant, it is common to either cover the nozzles of a printhead with tape or else to ensure that the printhead is otherwise covered with a cap. While such methods do slow the evaporation of solvents from the colorant, simply covering a nozzle is not sufficient to prevent the formation of accretions in a nozzle where the printhead is placed in storage for an extended period of time. Accordingly, there is a recognized need for a method and/or and apparatus that will prevent the formation of accretions in the nozzles of the printhead, particularly where the printhead must be stored for extended periods of time either before it is used or between uses.